1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for determining the location of a mobile terminal within a cellular network, and specifically to preventing the alteration of location information for mobile terminal-based location calculation methods.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) (terminal) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls the LA 18. Each Location Area 18 is divided into a number of cells 22.
Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless. The MS 20 may also include a Subscriber Identity Module (SIM) card 13, or other memory, which provides storage of subscriber related information, such as a subscriber authentication key, temporary network data, and service related data (e.g. language preference).
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS's 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN 10. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the MS's 20 currently located within the MSC/VLR area 12. If an MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 requests data about that MS 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
Determining the geographical position of a MS 20 within a cellular network 10 has recently become important for a wide range of applications. For example, positioning services may be used by transport and taxi companies to determine the location of their vehicles. In addition, for emergency calls, e.g., 911 calls, the exact location of the mobile terminal 20 may be extremely important to the outcome of the emergency situation. Furthermore, positioning services can be used to determine the location of a stolen car, for the detection of home zone calls, which are charged at a lower rate, for the detection of hot spots for micro cells, or for the subscriber to determine, for example, the nearest gas station, restaurant, or hospital, e.g., "Where am I" service.
MS-based location calculation methods have recently been developed whereby BTS 24 coordinates and other location information are transmitted to the MS 20 for calculation of the location of the MS 20. The MS 20 can then forward its location to a network location application that requested the positioning of the MS 20 or can use its determined location along with internal location applications to display the location information to the mobile subscriber.
For example, the MS 20 can have a Global Positioning System (GPS) receiver built into it, which is used to collect location information in order to allow the MS 200 to calculate its location. In addition, the MS 20 can collect positioning data based on the Observed Time Difference (OTD) between the time a BTS 24 sends out a signal and the time the MS 20 receives the signal. This time difference information can then be used by the MS 20 for calculation of the location of the MS 20.
By using Enhanced-OTD or GPS positioning methods with MS-based location calculation, it becomes unnecessary to have active two-way communication between the MS 20 and the network 14, which increases the signaling capacity of the network 14, and allows the MS 20 to perform location calculation while the MS 20 is in idle-mode. The implementation of MS-based location calculation is therefore expected to trigger a number of additional location applications, such as home zone charging, in which the price for using the voice or signaling channels can be dependent on the geographical location of the MS 20. However, when the MS 20 is responsible for calculating its position rather than the network, the system becomes volatile to fraud. For example, a mobile subscriber may be able to alter the real calculated location in order to apply a different (cheaper) tariff when using the voice or signaling channels.
It is, therefore, an object of the present invention to prevent the alteration of location information by the mobile subscriber when utilizing mobile terminal-based location calculation mechanisms.